Introduce safe interface to "copy and grow" FixedArray.

test/mjsunit/regress/regress-crbug-513507.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --noflush-optimized-code-cache --allow-natives-syntax
+
+// The following triggers a GC in SharedFunctionInfo::AddToOptimizedCodeMap.
+// Flags: --gc-interval=1234 --gc-global
+
+function makeFun() {
+  function fun(osr_fuse) {
+    for (var i = 0; i < 3; ++i) {
+      if (i == osr_fuse) %OptimizeOsr();
+    }
+    for (var i = 3; i < 6; ++i) {
+      if (i == osr_fuse) %OptimizeOsr();
+    }
+  }
+  return fun;
+}
+
+makeFun()(7);  // Warm up.
+makeFun()(4);  // Optimize once.
+makeFun()(1);  // Optimize again.